1. Field of the Invention
The present invention relates to a radiation image detection apparatus having a radiation image detector that generates electric charges by receiving a recording electromagnetic wave representing a radiation image and records the radiation image by storing the electric charges. The invention also relates to a manufacturing method of the radiation image detector.
2. Description of the Related Art
Various types of radiation image detectors that record a radiation image of a subject by receiving radiation transmitted through the subject have been proposed and put into practical use in medical and other fields.
For example, radiation image detectors using amorphous selenium that generates electric charges by receiving radiation are known, and a so-called TFT readout type is proposed as one of such radiation image detectors.
As for the TFT readout type radiation image detectors, for example, the following detector is proposed. That is, a detector that includes the following stacked on top of another: a bias electrode to which a bias voltage is applied; a photoconductive layer that generates electric charges by receiving radiation; and an active matrix substrate having multiple pixels disposed two-dimensionally, each with a charge collecting electrode for collecting the electric charges generated in the photoconductive layer, a storage capacitor for storing the electric charges collected by the charge collecting electrode, and a TFT switch for reading out the electric charges stored in the storage capacitor.
When recording a radiation image in the TFT readout type radiation image detector, radiation transmitted through a subject and representing a radiation image of the subject is irradiated on the radiation image detector from the bias electrode side, while, for example, a positive voltage is applied to the bias electrode from a power source.
The radiation irradiated on the radiation image detector transmits through the bias electrode, and is irradiated on the photoconductive layer. Then, electric charge pairs are generated in the photoconductive layer by the irradiation of the radiation, and the negative charges of the electric charge pairs are combined with positive charges charged on the bias electrode and dissolved, while the positive charges of the charge pairs are collected by each charge collecting electrode of each pixel of the active matrix substrate and stored in each storage capacitor as latent image charges, whereby the radiation image is recorded.
Thereafter, the electric charges stored in the storage capacitors are read out by turning ON the TFT switches on the active matrix substrate according to control signals outputted from a gate driver and the charge signals are detected by charge amplifiers, whereby image signals according to the radiation image are read out.
As one of the radiation image detectors using the active matrix substrate described above, for example, U.S. Pat. No. 6,642,534 proposes a radiation image detector that includes a bias electrode, a Se-based X-ray detection layer, a charge transport layer formed of Sb2S3, and an active matrix substrate stacked on top of another. The aforementioned patent publication describes that the provision of the charge transport layer may prevent injection of electron holes into the X-ray detection layer from the active matrix substrate, whereby image quality degradation is prevented.
In a radiation image detector having the charge transport layer, the interface between the charge transport layer and X-ray detection layer becomes the interface through which the electric charges generated in the X-ray detection layer by the irradiation of X-rays are transported. A study conducted by the inventor of the present invention, however, has revealed that impurities, such as oxygen, water, chloride compound, and the like, may sometimes deposit in the interface depending on the manufacturing method, whereby electric charges generated in the X-ray detection layer are trapped. The study has also revealed that the trap effect may give a favorable or unfavorable influence to the image quality depending on the position of the charge transport layer in the detector.
In view of the circumstances described above, it is an object of the present invention to provide a radiation image detection apparatus having a high image quality radiation image detector capable of appropriately controlling the charge traps described above. It is a further object of the present invention to provide a manufacturing method of the radiation image detector.